1. Field of the Invention
This invention relates to pneumatic tires, and more particularly to a pneumatic tire having high allweather type running performances and excellent wear resistance, or a pneumatic tire applicable as a passenger car bias tire, a passenger car radial tire or a motorcycle tire and having satisfactory running performances for providing sufficient road gripping force on dry road surfaces in fine weather, wet road surfaces in rainy weather and so-called ice snow road surfaces covered with ice and/or snow as well as excellent wear resistance.
2. Related Art Statement
Heretofore, there have been known various techniques for obtaining high running performance tires. For example, each of Japanese Patent laid open Nos. 55-60539 and 55-86827 discloses a tread rubber composition having an improved road gripping force on wet road surfaces by compounding a polymer having a high glass transition temperature so as to give a large loss factor around room temperature, for example, styrene-butadiene rubber having a high bound styrene content, or compounding large amounts of carbon black and oil in order to ensure a high road gripping force.
Further, there are known tires running on ice and snow roads or so-called snow tires and studless tires. For example, Japanese Patent laid open No. 59-206209 discloses a pneumatic tire having an improved road gripping force on ice and snow road surfaces by using a tread rubber composition consisting essentially of a polymer having a low glass transition temperature, i.e. a rubber selected from polybutadiene rubber, polyisoprene rubber and natural rubber.
Moreover, Japanese Patent laid open No. 62-62840 discloses a tire having high all-weather running performances by using a tread rubber composition compounded with an ester series low temperature softening agent.
The tread rubber disclosed in the above Japanese Patent laid open Nos. 55-60539 and 55-86827 cures at a low temperature, so that when the tire is run on icesnow road surfaces a sufficient friction force can not be given to the tire between the ground contact portion of the tire and the ground surface. Hence the running is not easy and also the wear resistance is insufficient.
On the other hand, the tire disclosed in the above Japanese Patent laid open No. 59-206209 exhibits satisfactory performances on ice-snow road surfaces, but has drawbacks as the wear resistance is poor and also sufficiently high running performances are not obtained because the hardness of the tread rubber around room temperature is too low and the friction coefficient of the tread rubber itself is low.
Moreover, the tire disclosed in the above Japanese Patent laid open No. 62-62840 is a tire having high all-weather running performances, but the wear resistance is not still sufficient.